Bruce wrote:
Soffit vents are 'required'.
Use the rigid foam panels that keep a clear air path over the insulation
where it meets your walls.

Also, if you use a swamp cooler, install a vented access door somewhere in
your living space that vents into the attic. When the cooler is on, the air
flows up into the attic (no need for an open window). With the cooler off,
the vent flaps close and block attic air from returning into the house.

A 'whole house fan' installed in the same way can be used to flush cool air
into the attic in the early morning and flush hot air out in the evening.

Where do you get those flap vents, and how well do they seal ?